Summary statement Robust model systems are essential for understanding human disease. While Alzheimer?s disease can be studied using in vivo models that have become more representative in recent years (e.g. by introducing natural genetic diversity and humanized APOE variants into existing Alzheimer?s mouse models), the ability to study vascular contributions to cognitive impairment and dementia (VCID) and cerebral small vessel disease (SVD) remains difficult. Indeed, the molecular mechanisms underlying VCID and SVD remain mostly unknown, and in vivo models for these diseases are lacking. A representative human in vitro model would therefore be beneficial to complement in vivo systems and improve understanding of vascular contributions to neurodegeneration. The development of human induced pluripotent stem cell (iPSC) technology has increased the utility of in vitro central nervous system (CNS) models, which have gradually progressed from isolated two-dimensional cell cultures to multi-cellular three-dimensional assemblies that better recapitulate the organization and architecture of specific brain regions. However, these human ?brain organoids? still have significant deficits. Notably, cortical organoids exhibit improperly organized laminar architectures and lack perfusable microvasculature with blood-brain barrier (BBB) function. These deficits limit the representativeness of using brain organoids to understand the mechanisms of VCID and SVD. In this proposed project, we will develop a biomimetic brain organoid platform with robust neurovascular function. Aim 1 of this proposal will characterize the organization and maturation of cortica. organoids grown in a novel biomaterial that mimics cues provided by radial glia to help guide laminar patterning. Aim 2 will focus on integrating brain endothelial cells and pericytes with the cortical organoids to develop perfusable microvasculature throughout the tissue construct, thereby generating the ?neurovascular organoid? platform. Aim 3 will then validate the representativeness of the neurovascular organoids by subjecting them to acute and chronic injuries known to damage the BBB; in particular, iPSCs with defined APOE genotype will be used to assess onset and progression of neurovascular dysfunction in response to this well-established genetic risk factor. Overall, this project will establish a human in vitro model of the vascularized cortex that is expected to have utility for unraveling the mechanisms of VCID and SVD.